June 16, 2011
Dwayne Brown
Headquarters, Washington
202-358-1726
dwayne.c.brown@nasa.gov
Paulette Campbell
Johns Hopkins University Applied Physics Laboratory, Laurel, Md.
240-228-6792
paulette.campbell@jhuapl.edu
RELEASE: 11-186
NASA SPACECRAFT CONFIRMS THEORIES, SEES SURPRISES AT MERCURY
WASHINGTON -- NASA scientists are making new discoveries about the
planet Mercury. Data from MESSENGER, the first spacecraft to orbit
Mercury, is giving scientists important clues to the origin of the
planet and its geological history and helping them better understand
its dynamic interior and exterior processes.
NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging
spacecraft, or MESSENGER, has been orbiting Mercury since March 18.
To date the spacecraft has provided tens of thousands of images
showing detailed planetary features. The planet's surface previously
had been seen only at comparatively low resolution but is now in
sharper focus.
The spacecraft also has collected extensive measurements of the
chemical composition of Mercury's surface and topography and gathered
global observations of the planet's magnetic field. Data now confirm
that bursts of energetic particles in Mercury's magnetosphere are a
continuing product of the interaction of Mercury's magnetic field
with the solar wind.
"We are assembling a global overview of the nature and workings of
Mercury for the first time," said MESSENGER principal investigator
Sean Solomon of the Carnegie Institution of Washington. "Many of our
earlier ideas are being cast aside as new observations lead to new
insights. Our primary mission has another three Mercury years to run,
and we can expect more surprises as our solar system's innermost
planet reveals its long-held secrets."
Flyby images of Mercury had detected bright, patchy deposits on some
crater floors. Without high-resolution images to obtain a closer
look, these features remained only a curiosity. Now new detailed
images have revealed these patchy deposits to be clusters of rimless,
irregular pits varying in size from several hundred feet to a few
miles wide. These pits are often surrounded by diffuse halos of more
reflective material and are found on central peaks, peak rings, and
rims of craters.
"The etched appearance of these landforms is unlike anything we've
seen before on Mercury or the moon," said Brett Denevi, a staff
scientist at the Johns Hopkins University Applied Physics Laboratory
(APL) in Laurel, Md., and a member of the MESSENGER imaging team. "We
are still debating their origin, but they appear to be relatively
young and may suggest a more abundant than expected volatile
component in Mercury's crust."
One of two instruments on the spacecraft designed to measure the
quantity of key chemical elements on Mercury has made several
important discoveries since the orbital mission began. Elemental
ratios averaged over large areas of the planet's surface show that
Mercury's surface differs markedly in composition from that of the
moon.
Observations have revealed substantial amounts of sulfur at Mercury's
surface, lending support to prior suggestions from ground-based
telescopic observations that sulfide minerals are present. This
discovery suggests that the original building blocks from which
Mercury formed may have been less oxidized than those that formed the
other terrestrial planets. The result also hints that
sulfur-containing gases may have contributed to past explosive
volcanic activity on Mercury.
Topography data of Mercury's northern hemisphere reveal the planet's
large-scale shape and profiles of geological features in high detail.
The north polar region is a broad area of low elevations, whereas the
overall range in topographic heights seen to date exceeds 5 miles (9
kilometers).
Two decades ago, Earth-based radar images showed deposits thought to
consist of water ice and perhaps other ices near Mercury's north and
south poles. These deposits are preserved on the cold, permanently
shadowed floors of high-latitude impact craters. MESSENGER is testing
this idea by measuring the floor depths of craters near Mercury's
north pole. The craters hosting polar deposits appear to be deep
enough to be consistent with the idea that those deposits are in
permanently shadowed areas.
During the first of three Mercury flybys in1974, Mariner 10 discovered
bursts of energetic particles in the planet's Earth-like
magnetosphere. Four bursts of particles were observed on that flyby.
Scientists were puzzled that no such strong events were detected by
MESSENGER during any of its three flybys of the planet in 2008 and
2009. But now that the spacecraft is in near-polar orbit around
Mercury, energetic events are being seen regularly.
The spacecraft was designed and built by APL. The lab manages and
operates the mission for NASA's Science Mission Directorate (SMD) in
Washington. The mission is part of NASA's Discovery Program, managed
for SMD by the agency's Marshall Space Flight Center in Huntsville,
Ala.
For more information about the mission, visit:
http://www.nasa.gov/messenger
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